In internal combustion engines equipped with a charger, the latter directs air under elevated pressure to the combustion chambers of the engine to increase the power delivered thereby and it is known to switch in the charger as required to obtain the increased power. For example, this was done with the earliest compressor motors. The compressor could be arbitrarily switched in by the driver as deemed necessary; however, this could be done for only a short time in order to prevent damage to the motor.
The most common present day chargers are turbochargers, which are driven at high rotational speeds by a turbine wheel of the engine and deliver pre-pressurized air to the combustion chamber of the engine. A disadvantage here is the relatively abrupt switch-in of the charger after a predetermined rotational speed (rpm) threshold has been reached. Beneath this threshold the internal combustion engine does not offer any substantial power because of the low initial pressurization at a comparatively low operating efficiency.